Electrical Discharge Machining (EDM) VS Electrochemical Machining (ECM)
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Both EDM and ECM are non-conventional machining methods; however, both processes have considerable differences. EDM, or electrical discharge machining, relies on localized spark erosion to remove material, whereas ECM, or electrochemical machining, utilizes electrolysis to dissolve the metal locally. The table below is a short summary comparing the two processes; keep reading to explore some of the other differences, similarities, and advantages of each in more detail.
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EDM | ECM | |
Process Summary | EDM removes material via heat from rapid electrical discharges. | ECM dissolves material with an electrochemical reaction. |
Fluid | Dielectric fluid utilized, such as deionized water, with the purpose of controlling electrical discharges to maintain accuracy. | Electrolytic fluid, such as NaNO3, utilized as both a catalyst for electrochemical reaction and flushing agent for material waste. |
Costs | Relatively low NRE with higher cost production. | Relatively high NRE with lower cost production. |
Current | 50-400V; 100-200 amps. | >50V with high current. |
Tool | Continuous tool wear. | No tool wear. |
Machining Method | Spark ablation. | Electrochemical reaction. |
Finishing | 6-.8 Ra is typical. | .4 to .2 µm Ra is typical. |
DIFFERENCES
In addition to the metal removal method, there are some other fundamental process differences.
Working fluid: EDM utilizes a dielectric fluid, usually deionized water or a hydrocarbon compound of sorts. This serves several purposes, all serving the ultimate goal of controlling electrical discharges to maintain accuracy removing material during the process. In order to get a high current density in the plasma channel, the fluid separates the working electrodes. It also helps prevent particle linkages that could short circuit and interrupt the process when it flushes the area. ECM, on the other hand, (both enable non contact process but mechanism is different) uses an electrolyte solution, helping perform the same task as a dielectric fluid, but in the opposite way. A salt-based liquid such as NaNO3 or NaCl covers the process and conducts electric currents between the cathode (the tool) and the anode (what is being worked on). The DC current gives the anode a positive electrode charge, allowing it to be oxidized. This oxidization is then stripped away (and flushed out with the solution) leaving an extremely smooth finish without any burrs or a recast layer.
Power level: EDM's voltage can be anywhere from 50 to 400 Volts, generating tremendous energy in a spark. emitting a lower current ECM, though, is a low voltage, high current process-- electricity is being conducted through the electrolyte solution, carrying a much higher current than with EDM.
Tooling: Although neither process involves direct contact between the cathode and anode, EDM exhibits tool wear and ECM does not. Simplified, this is due to substantial heat in EDM that slowly alters the tool and the workpiece. ECM, however, doesn't have a chemical reaction that erodes the tool; therefore a tool could theoretically create infinite parts under ECM.
SIMILARITIES
Non-contact process: the tool or electrode does not come into contact with the work piece. A small gap is maintained and flushed with the working fluid.
Electrical energy: Both processes require a power source, typically a pulsed DC power supply, to enable the metal removal.
Conductive materials: In general, both processes are limited to processing electrically conductive materials.
ECM - ADVANTAGES
The electrochemical machining process can be thought of as reverse electroplating; instead of adding material, metal is dissolved and carried away by a flowing electrolyte.
Non-thermal machining: No thermal-related stress means the material properties of the surface remain unchanged after ECM. This also means no heat-affected zone (HAZ). A particular disadvantage comes with a 'recast layer' in EDM, where the process will strip material off of the workpiece, but because it remains hot it can actually re-weld itself back onto the surface, creating undesirable irregularities.
Surface finish: The ECM process is capable of very low surface roughness values. The achievable results can be compared to electropolishing; however, shape formation is achieved simultaneously. ECM also doesn't require a finishing pass or finishing electrode.
Volume production: The lack of tool wear makes the ECM process well-suited for volume production. Although the initial development costs can be high, the return on investment can be quickly realized in production.
Process speed: ECM removes material continuously from all surfaces that are in close proximity to the electrode. Provided there is sufficient electrolyte flow and available electrical amperage, the ECM removal rate scales linearly with surface area of the electrode. For example, we could drill 1 hole at 1 mm/min or we could drill 100 holes at 1 mm/min (equivalent of 1 hole at 100 mm/min).
EDM - ADVANTAGES
The electrical-discharge machining process is much more common and can be found in many standard machine shops across the country. Therefore, it possesses two large advantages over ECM.
Low initial cost: Many years of process development and refinement have resulted in a process that is very well understood. As a result, the tool geometry can easily be designed and fabricated to support the EDM process with relatively low risk. This, in addition to the wide availability of equipment, drives the initial cost down.
Prototype quantities: Tangential to the low initial cost, EDM is well suited for low volume or prototype quantities. However, tool wear is continuous and as a result, it needs to be replaced on a regular interval. This does not prevent EDM from being used in production but does result in additional cost and time.
At Voxel we recognize that there are numerous ways to fabricate a part and that neither of these solutions is superior in all cases. Each and every application has unique challenges that may make it well-suited for a specific fabrication process. We are happy to discuss your application with you and determine the best manufacturing process to achieve your desired results.
This article is part of our ongoing “PECM vs. Competing Processes” series that compares PECM to other, popular machining processes. Find other articles in the series below:
CNC Milling vs. ECM
Electropolishing vs. ECM
Photochemical Etching vs. ECM